1. Field of the Invention
The present invention relates to a mechanism that conveys sheets using a roller or a guide.
2. Description of the Related Art
Image forming apparatuses such as MFPs (Multifunction Peripherals) and sheet conveying mechanisms are improved so as to reduce possible noise. Most of the improvements for reducing possible noise are collision sound or flopping sound preventing measures for preventing a possible collision sound generated when a guide collides against a sheet or sound insulating or absorbing mechanisms that block gaps through which sound leaks. However, these measures require an additional material typified by a sound absorbing material, which requires new costs. In spite of the capability of reducing the collision sound, the measures for collision prevention and the like may degrade conveying performance if the method of the measure is inappropriate. A known method for reducing costs with the appropriate conveying performance maintained is Helmholtz resonance (intra-cavity resonance at a particular frequency) utilizing sound interference and typified by Japanese Patent No. 3816678. Specifically, this method provides a resonance space and makes a hole in the resonance space so that sound can be transmitted through the hole, to reduce a prevailing periodic sound. The method is effective on discrete periodic sounds (one frequency prevails significantly) resulting from rotation, such as an electromagnetic sound from a motor or a whirling sound from a fan. However, a sheet conveying noise made up of a plurality of noises such as a roller rotation sound, a paper rubbing sound, and a fan disturbance noise is not limited to the periodic sound but is distributed over a wide band. Thus, the application of the measure disclosed in Japanese Patent No. 3816678 is not expected to reduce the possible noise over a wide band.
Most of the improvements for reducing possible noise in the sheet conveying mechanism are sheet collision and flopping sound preventing measures using a guide or sound insulating or absorbing mechanisms that block gaps. However, these measures require new costs typified by a sound absorbing material, and may degrade the conveying performance depending on the method of the measure. Shape improving measures utilizing Helmholtz resonance improve the shape of the apparatus while avoiding degradation of the conveying performance and increasing the costs. The shape improving measures are effective on the discrete periodic sound but have difficulty reducing possible noise over a wide band. Thus, measures are required which improve the shape of the apparatus while avoiding the use of a new material such as a sound absorbing material, to reduce the costs and which reduce possible noise distributed over a wide band in addition to the periodic sound.
Furthermore, as is well known, when a bulging space is present in the conveying path, noise passing through the space tends to become louder. The bulging space is often provided in the conveying path because the space is required not only to reduce possible noise but also to assist the conveyance of sheets. In connection with the maintenance of the appropriate conveying performance, the bulging space cannot be simply closed. Thus, measures are also required which improve the conveying path to inhibit an increase in the level of noise in the bunging space.
As described above, most of the noise reducing means in the sheet conveying mechanism is the sheet collision and flopping sound preventing measures using the guide or the sound insulating or absorbing mechanisms that block the gaps. However, these measures require new costs typified by the sound absorbing material, and may degrade the conveying performance depending on the method of the measure. The shape improving measures utilizing the Helmholtz resonance improve the shape of the apparatus while avoiding degradation of the conveying performance and increasing the costs. The shape improving measures are effective on the discrete periodic sound but have difficulty reducing the possible noise over a wide band. Thus, the measures are required which improve the shape of the apparatus while avoiding the use of the new material such as the sound absorbing material, to reduce the costs and which reduce the possible noise distributed over a wide band in addition to the periodic sound.
Furthermore, as is well known, when the bulging space is present in the conveying path, the noise passing through the space tends to become louder. For purposes including a reduction in possible noise, the bulging space is often provided in the conveying path. The bulging space cannot be simply closed. Thus, the measures are also required which improve the conveying path to inhibit an increase in the level of noise in the bunging space.